Method for making a composite airfoil

ABSTRACT

A method of manufacturing a composite airfoil includes the step of providing a core made of a metal or ceramic material. A plastic airfoil portion is molded to envelope at least a portion of the core.

FIELD OF THE INVENTION

The invention relates generally to turbo-machinery. In particular, the invention relates to making a turbo-machine airfoil with components of different materials.

Turbo-machinery may take many forms or be applied in various uses. These forms and uses may include steam turbines for power generation, gas turbines for power generation, gas turbines for aircraft propulsion and wind turbines for power generation.

In a gas turbine, typically there are numerous rotating blades and stationary vanes. The blades and vanes are arranged in alternating circumferential arrays that are spaced longitudinally along the turbine. Each of the blades and vanes includes an airfoil portion attached to a mounting portion.

A conventional gas or stream turbine blade or vane design typically has its airfoil portion made entirely of an alloy of a metal, such as titanium, aluminum or stainless steel. The conventional gas or steam turbine compressor blade or vane design may also be made entirely of a composite, such as fiber reinforced plastic. The all-metal blades are relatively heavy in weight that can result in lower fuel economy and require robust mounting portions. In a gas turbine application, the lighter all-composite blades are susceptible to damage and wear from foreign object ingestion.

Known hybrid blades include a composite airfoil portion having a metal leading edge to protect the airfoil from wear and impact from foreign object ingestion. The gas turbine first stage blades typically are the largest and the heaviest blades and are generally the first to be subject to foreign object ingestion. Composite blades have typically been used in turbine applications where weight is a major concern.

On a typical gas turbine compressor airfoil, the overall geometry is a compromise between structural and aerodynamic needs. Structural needs and ability to withstand damage due to foreign object ingestion are in direct conflict with airfoil geometry optimized for aerodynamic performance. For example, an aerodynamically desirable airfoil is relatively thin with a relatively sharp leading edge. Whereas, a structurally desirable airfoil is relatively thick with a robust leading edge. The final design is typically a compromise between the opposing structural and aerodynamic needs with neither being optimum.

Current manufacturing processes for an all-metal airfoil requires milling and hand polishing of the airfoil to achieve the desired geometry. The polishing operation is labor intensive to achieve critical airfoil dimensions and surface finish. This requires usage of materials that are easily machined and polished to minimize cost. This typically restricts material selection and increases the cost of manufacturing.

During operation of a gas turbine for power generation, dirt and debris accumulate on the airfoil surface resulting in a loss of designed performance. Water washing is typically used to remove this accumulated dirt and debris. Such washing may erode and corrode the metal material of the airfoil. Compressor tip clearances are typically not optimized to preclude the chance of rotor blade tips rubbing on the case or stator blade tips rubbing on the rotor.

Accordingly, there is a need for an improved turbine airfoil for a gas turbine blade that is lighter in weight than an all-metal airfoil, possesses desirable structural and aerodynamic properties, withstands foreign objects ingestion, be cost effective and resist erosion and corrosion.

SUMMARY

A method of manufacturing a composite airfoil according to one aspect of the invention includes the step of providing a core made of a metal or ceramic material. A plastic airfoil portion is molded to envelope at least a portion of the core.

Another aspect of the invention is a method of manufacturing a composite airfoil. The method includes the step of providing a core made of a metal or ceramic material. The core is provided with a leading edge. A plastic airfoil portion is molded to envelope at least the leading edge of the core.

Another aspect of the invention is a method of manufacturing a composite airfoil. The method includes the step of forming a metal core by die casting, investment casting or forging. A plastic airfoil portion is injection molded to envelope at least a portion of the core.

DRAWINGS

These and other features, aspects, and advantages of the invention will be better understood when the following description is read with reference to the accompanying drawings, in which:

FIG. 1 is a perspective illustration of a composite airfoil according to one aspect of the invention, with an internal component represented by dashed fines;

FIG. 2 is an exploded view of the composite airfoil illustrated in FIG. 1; and

FIG. 3 is a cross-sectional view of the composite airfoil of FIG. 1, taken approximately along line 3-3 in FIG. 1.

DETAILED DESCRIPTION

A composite airfoil 20 is illustrated in FIG. 1 as a part of a blade 10 for a gas turbine used in a power generation application, according to one aspect of the invention. It will be appreciated that the composite airfoil 20 of the blade 10, in various aspects of the invention, may be in the form of a compressor blade, vane or turbine blade and may be used in steam turbine, gas turbine or wind turbine applications. The composite airfoil 20 of the blade 10, according to one aspect, includes a core 22 and a plastic airfoil portion 24 completely enveloping and encapsulating the core.

The composite airfoil 20 is made from at least two different materials in a unique manner. As used herein, “composite” is defined as having a plastic material form the finished airfoil portion 24 located over a relatively strong structural material that (such as, metal or ceramic) forms the core 22. The term “plastic” is defined to mean capable of being melted at a temperature relatively lower than the melting point of the material of the core 22 so it can flow and easily be molded to a final desired shape.

A root 26 is attached to the core 22 and is used to mount the blade to turbine structure for operation. The root 26 can be attached to the core by forming the core and root integrally as a one-piece subcomponent, such as by forging or machining from a single piece of raw material, such as metal or ceramic. Alternatively the core 22 and root 26 could be made separately and the core could be fastened, welded or otherwise attached to the root. A tip 40 is located at the axially opposite end of the composite airfoil 20 from the root 26. An axis A extends in a direction along the length of the composite airfoil 20 from the root 26 to the tip 40. As used herein, “axis” A refers to reference axis and not a physical part of the blade 10 or composite airfoil 20.

The blade 10 and composite airfoil 20 are a designed to operate at the typical temperature that the first few stages of a turbine compressor would be exposed to according to one aspect of the invention. In a gas turbine application for power generation the “design operating temperature” is the maximum temperature the blade 10 and airfoil portion 24 is expected to experience during normal operation in the first few stages in a compressor. An example of a typical gas turbine design operating temperature in the first few stages is, without limitation, generally in the range of 18° C. to 200° C.

Medium direction arrows M in (FIG. 3) indicate the general direction of flow. The medium M typically comprises air in a gas turbine application. The medium M in a gas turbine power generation application is typically controlled. Specifically, the medium M is inlet air filtered to remove many of the foreign objects, can be chilled or heated to a desired temperature range and routed through structure to remove moisture and salt.

In a compressor blade application of a gas turbine for the composite airfoil 20, the root 26 typically includes a dovetail portion 42 (FIGS. 1-2), to mount the blade 10 to a rotor disc (not shown). The airfoil portion 24 has a leading edge 44 (FIG. 3) and a trailing edge 46. The direction of medium M flow is generally from the leading edge 44 to the trailing edge 46. The airfoil portion 24 of the composite airfoil 20 also has a pressure side surface 62 and a suction side surface 64.

The airfoil portion 24 is a very complex surface defined by a series of points at sections spaced along the axis A. The leading edge 44 and trailing edge 46 are typically round surfaces defined by relatively small radii according to one aspect of the invention. The complex surface, leading edge 44 and trailing edge 46 are relatively difficult to manufacture. For aerodynamic reasons, it is generally desirable to have a leading edge 44 with as small of a radius as possible, for example 0.010 inch which has not been practical previously. It is also desirable to have an extremely smooth and precise final shape for the airfoil portion 24 that does require machinery polishing or coating, which also has not been practical previously. Being able to injection mold a plastic airfoil portion 24 to a final or near-final shape overcomes previous disadvantages.

Preferably, the airfoil portion completely envelopes the core 22. In one aspect of the invention, the composite airfoil 20 is the plastic airfoil portion 24 enveloping at least a portion of the metal or ceramic core 22. It will be apparent, however, that the core 22 does not have to be completely enveloped by the airfoil portion 24 and that the core may be partially covered according to another aspect of the invention. The plastic airfoil portion 24 is molded without the need for fiber reinforcement, preferably injection molded, onto at least a portion of the core 22. The injection molding process is capable of forming precise and accurate parts of the airfoil portion 24, such as the pressure side surface 62, suction side surface 64, leading edge 44 and trailing edge 46.

With the multi-piece design the internal geometry of the blade 10 in the form of the core 22 can be optimized for frequency tuning and structural needs. The external surface can be tailored for aerodynamic performance in the form of the injection molded plastic airfoil portion 24.

In an exemplary aspect the core 22 has a plurality of openings 82 extending through it between the pressure side surface 62 and suction side surface 64 of the airfoil portion 24. The openings 82 are located in areas of the core 22 that do not need a continuous solid structure for strength or function. The openings 82 lighten the core 22 for lower rotating mass which is generally a desirable feature. The openings 82 receive a portion 84 of the plastic material of the airfoil portion 24 during the injection molding process to retain the airfoil portion in place relative to the core 22. The openings 82 do not have to extend completely through the core 22 but have a depth sufficient to receive portion 84 of the plastic material. The portion 84 of plastic material does not have to completely fill the opening 82 but extend a sufficient distance in to the opening to retain the airfoil portion 24 in place relative to the core 22.

The core 22 has a tip portion 100 (FIG. 2). The core 22 has a leading edge 102 (FIGS. 2 and 3) and a trailing edge 104. The tip 28 of the airfoil portion envelopes the tip portion 100 of the core 22. The airfoil portion 24 envelopes at least the leading edge 102 of the core 22 and preferably the entire outer surface of the core including the trailing edge 104. The airfoil portion 24 has a thickness t (FIG. 3) at a location spaced away from the openings 82 such as in the range of 0.020 to 0.100 inch to where it covers the core 22 away from the openings 82. The thickness to does not have to be uniform. The thickness t may gradually increase from one or both edges 44, 46 towards the middle of the blade 10. The depth of the opening 82 is preferably greater than the thickness t of the airfoil portion 24 covering the core 22.

By creating the airfoil portion 24 from plastic, desired final airfoil shape for aerodynamic performance can be incorporated and preferably without the need form machinery, polishing or coating. Since the airfoil portion 24 is separated from the internal load carrying structure of the core 22 a design that is more tolerant to damage from ingested debris is also possible. This separation of load carrying structure of the core 22 from the airfoil portion 24 also increases the number of material options available for manufacturing the core to maximize structural features and minimizing weight.

By disassociating the structural and aerodynamic components of the design of the blade 10, a number of cost savings opportunities arise. Tight manufacturing tolerances are no longer required on the internal load carrying structure that now permits the usage of nickel or ceramic materials for the core 22. The materials with higher modulii can provide similar stiffness with less mass reducing the overall weight of the blade 10. This also opens up the potential for investment casting, die casting or forging of the core 22 with limited machining. Injection molding the plastic airfoil portion 24 to provide the final aerodynamic shape can eliminate the entire hand polishing operation of previous all-metal blade configurations. Injection molding the plastic airfoil portion 24 also yields a very consistent airfoil shape with an excellent surface finish eliminating the need for any surface treatments after polishing.

Creating a smooth surface for the plastic airfoil portion 24 from injection molding will reduce accumulation of debris on the blade 10. This reduces the need for as frequent water washes. The material for the plastic airfoil portion 24 is inherently corrosion resistant. Additionally, additives such as PTFE can be introduced into the airfoil portion 24 to further enhance the repelling of the accumulation of debris on the airfoil portion.

By injection molding the tip 28 of the plastic airfoil portion 24 the clearances relative to other turbine components can be held tighter. In the event the plastic nibs against another turbine component, it is a benign event and does not compromise the structural components of the blade 10 or turbine. With the composite airfoil 20 compressor clearances can be held tighter for improved performance without the need of abradable surfaces or the introduction of rub compliant coating.

The technical advantages are numerous. The composite airfoil 20 provides the opportunity to create more damage tolerant and optimized airfoil portion 24 and a structurally optimized core 22. Additionally the opportunity to optimize aerodynamic geometry of the airfoil portion 24 results in increased performance of the gas turbine. Reduction of compressor fouling of the airfoil portion 24 reduces the level of performance degradation. There are also significant opportunities to reduce manufacturing costs.

The composite airfoil 20 of the blade 10, thus, provides an optimal aerodynamic shape with the injection molded plastic airfoil portion 24 and desired structural characteristics with the core 22. The plastic material of the airfoil portion 24 may be any suitable plastic material. The plastic material is selected to be able to survive the design operating temperature of the particular stage of the turbine that it is selected to operate in. For example, the first stage of a gas turbine compressor operates at ambient air temperatures and at relatively low pressures compared to other later stages of the compressor.

The blade 10 can be manufactured according to another aspect of the invention. The blade 10 is made with the composite airfoil 20 by first forming the metal core 22 by die casting, investment casting or forging. The core 22 may also be made from a ceramic material cast to final shape. The core 22 is formed with the root 26 and dovetail portion 42 in its final configuration.

The core 22 is then supported in a die 120 (FIG. 4) of an injection molding apparatus (not shown). The die 120 of the injection molding apparatus has a desired shape of half of the airfoil formed in the die with allowances for shrinkage and warping. The core 22 is supported in a predetermined position within the die, as illustrated in FIG. 5. Locator pins 140 in the die 120 assist in properly locating the core 22 in a predetermined position relative to the airfoil shape. A vent 122 extends from the interior of the die to the outside. The root 26 may be located outside of the die 120 and have a surface that engages the die to locate the core 22 axially relative to the die.

A second die 126 (FIG. 6) is provided. The second die 126 of the injection molding apparatus has a desired shape of another half of the airfoil formed in the die with allowances for shrinkage and warping. A vent 122 extends from the interior of the second die 126 to the outside. The second die 126 is moved to engage the die 120 and enclose the core 22. A conduit 124 is provided to direct melted material into the cavity created by the dies 120, 126.

The airfoil portion 24 is then injection molded to envelope at least a portion of the core 22. The airfoil portion 24 is made from a plastic material. The plastic material is melted in the injection molding apparatus. The melted plastic is forced into the dies 120, 126 through the conduit 124. The plastic material then cools and hardens to form the desired shaped formed by the cavity of the dies 120, 126 around the core 22.

The core 22 has a plurality of voids or openings 82 formed in the core. During the injection molding process, the openings 82 in the core 22 are filled with the melted plastic material of the airfoil portion 24. This retains the airfoil portion 24 in a position relative to the core 22.

Specific terms are used throughout the description. The specific terms are intended to be representative and descriptive only and not for purposes of limitation. The invention has been described in terms of at least one aspect. The invention is not to be limited to the aspect disclosed. Modifications and other aspects are intended to be included within the scope of the appended claims. 

1. A method of manufacturing a composite airfoil, the method comprising the steps of: providing a core made of a metal or ceramic material; and molding a plastic airfoil portion to envelope at least a portion of the core.
 2. The method of claim 1 further including the step of providing at least one opening in the core and the molding step includes filling the at least one opening with the plastic material of the airfoil portion to retain the airfoil portion in a position relative to the core.
 3. The method of claim 1 wherein the core is provided with a leading edge and the molding step comprises injection molding the airfoil portion to envelope the leading edge of the core.
 4. The method of claim 1 wherein the molding step comprises injection molding the airfoil portion to completely envelope the core.
 5. The method of claim 4 wherein the injection molding step includes the step of providing a final shape and finish to the airfoil portion.
 6. The method of claim 1 wherein the providing step comprises providing a metal core by a process selected from die casting, investment casting and forging.
 7. A method of manufacturing a composite airfoil, the method comprising the steps of: providing a core made of a metal or ceramic material, the core provided with a leading edge; and molding a plastic airfoil portion to envelope at least the leading edge of the core.
 8. The method of claim 7 further including the step of providing at least one opening in the core and the molding step includes filling the at least one opening with the plastic material of the airfoil portion to retain the airfoil portion in a position relative to the core.
 9. The method of claim 7 wherein the molding step comprises injection molding the airfoil portion.
 10. The method of claim 7 wherein the molding step comprises injection molding the airfoil portion to completely envelope the core.
 11. The method of claim 10 wherein the injection molding step includes the step of providing a final shape and finish to the airfoil portion.
 12. The method of claim 7 wherein the providing step comprises providing a metal core by a process selected from die casting, investment casting and forging.
 13. A method of manufacturing a composite airfoil, the method comprising the steps of: forming a metal core by die casting, investment casting or forging; and injection molding a plastic airfoil portion to envelope at least a portion of the core.
 14. The method of claim 13 further including the step of forming at least one opening in the core and the injection molding step includes filling the at least one opening with the plastic material of the airfoil portion to retain the airfoil portion in a position relative to the core.
 15. The method of claim 13 wherein the core is provided with a leading edge and the injection molding step comprises enveloping the leading edge of the core with plastic material.
 16. The method of claim 13 wherein the injection molding step comprises completely enveloping the core.
 17. The method of claim 13 wherein the injection molding step includes the step of providing a final shape and finish to the airfoil portion. 